1. Field of the Invention
The present general inventive concept relates to a power transmission. More particularly, the present general inventive concept relates to a power transmission using a friction roller, a medium discharging apparatus having the power transmission, and an image forming apparatus having the medium discharging apparatus.
2. Description of the Related Art
Generally, methods are known which transmit a driving force of a driving roller to a driven roller in an image forming apparatus, such as a printer, a copier, or the like, using a gear, a method using a belt, a method using a friction roller, etc. Among these methods, the method using the friction roller is popularly used, in that it generates relatively low noise, simplifies construction, and minimizes space utilization, as compared with other methods.
FIG. 1 is a view schematically exemplifying an example of an image forming device in which a power transmission using a general friction roller is employed. In FIG. 1, reference numerals 10, 20, 30, 40, and 50 represent an image forming unit, a medium supplying unit, a driving roller, a driven roller, and a friction roller, respectively.
The driving roller 30 is rotated by a driving source, which is not illustrated. A rotating force of the driving roller 30 is transmitted to the driven roller 40 by the friction roller 50, and thus the driven roller 40 is rotated along with the driving roller 30 to convey a printing medium P supplied from the medium supplying unit 20.
The friction roller 50 is elastically urged upward by a pressing spring 60, so that it comes in contact with the driving roller 30 and the driven roller 40. To increase a friction force, the rollers 30, 40, and 50 are formed of a rubber roller or a surface-treated metal shaft.
However, the power transmission using the general friction roller as described above is configured to press the friction roller 50 against the driving roller 30 and the driven roller 40 through the pressing spring 60. Accordingly, the power transmission may generate a power loss. To compensate for the power loss, the power transmission needs a large driving source, thereby resulting in an increase in costs.